A cleaning method for through-hole plating of a flexible wiring board

Abstract

The present application relates to printed circuit board technical field, disclose a kind of cleaning method for flexible circuit board via electroplating, comprising the following steps;Soft plate cutting→drilling→plasma processing→first time film pasting process (whole plate film pasting)→first exposure and development (exposed the via position needing electroplating)→automatic optical inspection→thin plate vertical continuous electroplating (copper plating hole)→film stripping→graphic transfer process (including second time film pasting, exposure, development)→laser cleaning removes hole dry film residue;Hole dry film cleaning is carried out using laser drill, can efficiently, accurately remove the dry film residue in hole, improve production efficiency;By accurately control laser energy and aperture size, can avoid damage to copper surface, guarantee the integrity of FPC product;The complete cleaning of hole dry film can ensure the uniform filling of resin in subsequent pressing process of flexible core plate, avoid problems such as cavity, burst layering, improve the reliability of FPC product.

Description

Technical Field

[0001] The invention relates to the technical field of printed circuit boards, and in particular to a cleaning method for through-hole electroplating of a flexible circuit board. Background Art

[0002] As electronic products advance towards miniaturization and higher density, flexible printed circuit boards (FPCs) are widely used due to their excellent flexibility and high integration. However, the diameter of interlayer vias in FPCs has gradually decreased from 300 microns to 100 microns or less, posing a significant challenge to through-hole electroplating technology. Existing technologies, while full-board copper plating and localized patterned hole electroplating methods, have to some extent met the requirements of conventional FPC products.

[0003] However, for FPC products with special requirements for fine circuits or impedance, the current FPC hole plating process is: flexible board cutting → drilling → plasma → first film lamination process (whole-plate lamination) → first exposure and development (exposing the through-hole position to be plated) → automatic optical inspection → thin plate vertical continuous electroplating (hole copper plating) → film stripping → pattern transfer process (including second film lamination, exposure, and development);

[0004] Due to the reduction in the aperture, the developer becomes difficult to flow in the hole during the second development, which increases the difficulty of dry film removal. During the lamination and exposure process of the 0.05mm ultra-thin flexible core board, the step after the hole plating may cause the upper and lower layers of dry film to stick together. The adhesion between the dry films will increase the difficulty of film removal, resulting in dry film residue after graphic production. The hole plating of flexible circuit boards is generally thin. Conventional film stripping lines are used again or at a slower speed. In addition, organic film stripping lines are not only unable to remove the film completely, but also bring the risk of board folding due to the thin board. This problem will seriously affect the resin filling in the subsequent lamination process. If the resin cannot completely fill the hole, it will form voids or bubbles, or even delamination, reducing the mechanical strength and electrical performance of the circuit board and affecting product reliability.

[0005] In order to solve the above-mentioned problems, we need to propose a cleaning method for through-hole electroplating of flexible circuit boards to solve the problem of unclean film removal in the holes after hole plating and ensure the reliability and quality of FPC products. Summary of the Invention

[0006] The purpose of the present invention is to provide a cleaning method for through-hole electroplating of flexible circuit boards. A laser drill is used to clean the dry film in the hole, which can efficiently and accurately remove the dry film residue in the hole, thereby improving production efficiency. By precisely controlling the laser energy and aperture size, damage to the copper surface can be avoided, thereby ensuring the integrity of the FPC product. The thorough cleaning of the dry film in the hole can ensure the uniform filling of the resin during the subsequent pressing process of the flexible core board, avoid problems such as voids, board explosion and delamination, and improve the reliability of the FPC product. The method is suitable for various types of flexible printed circuit boards, especially FPC products with special requirements for fine circuits or impedance. It is easy to operate, efficient, and suitable for large-scale production applications to solve the problems raised in the above-mentioned background technology.

[0007] To achieve the above-mentioned object, the present invention provides the following technical solution: a method for cleaning through-hole electroplating of a flexible circuit board, comprising the following steps;

[0008] S1. Flexible core board cutting: According to the design requirements of the flexible printed circuit board, use professional cutting equipment to accurately cut the raw materials to obtain the required flexible board size;

[0009] S2. Drilling: Drill through holes with a diameter of 0.15-0.3mm on the flexible printed circuit board according to customer requirements;

[0010] S3, Plasma treatment: Use plasma cleaning technology to clean the soft board after drilling, remove burrs, dirt and oxides generated during the drilling process, and ensure the hole wall is smooth and clean;

[0011] S4. First lamination: Lamination is performed on the entire flexible printed circuit board after cleaning, ensuring that the dry film is evenly covered on the board surface without bubbles;

[0012] S5. First exposure and development: Through the exposure and development process, the unnecessary parts on the dry film are removed to expose the through-hole positions that need to be electroplated;

[0013] S6. Automatic optical inspection: Use automatic optical inspection equipment to inspect the flexible printed circuit board after exposure and development to ensure the accuracy of the through-hole dry film window pattern and the cleanliness of the through-hole;

[0014] S7, thin plate vertical continuous electroplating (hole copper plating): the qualified flexible printed circuit board is sent to the thin plate vertical continuous electroplating equipment for hole copper plating. Through electroplating, it is ensured that the inner wall of the through hole is evenly covered with a layer of copper;

[0015] S8, film stripping: After the electroplating is completed, the flexible printed circuit board is stripped to remove the unnecessary dry film on the circuit board;

[0016] S9, pattern transfer process: After the film is removed, the pattern transfer process is carried out. The pattern transfer process includes the second film application, exposure and development to form the final circuit pattern;

[0017] S10. Laser cleaning to remove dry film residue in the hole: Use a laser drill to clean the dry film residue in the hole to remove the dry film residue in the hole.

[0018] Preferably, in step S1, the process of cutting the flexible core board is as follows:

[0019] S11. Before cutting, check the flatness, thickness, surface damage and contaminants of the flexible board;

[0020] S12, parameter setting, setting the size, shape and precision of the flexible core board cutting, and adjusting the cutting speed, cutting depth and pressure parameters of the cutting machine;

[0021] S13. Positioning of flexible core board: Use the positioning fixture to fix the flexible core board on the working table of the cutting machine and ensure that the position and positioning angle of the flexible core board are correct;

[0022] S14, cutting operation: operate the cutting machine to cut the flexible core board and observe the cutting condition during the cutting process.

[0023] Preferably, in step S2, when drilling holes on the flexible printed circuit board, a drill bit with a diameter of 0.15-0.3 mm is selected and installed on the drilling rig, and the power and speed of the drill bit are controlled according to the thickness and hardness of the flexible printed circuit board to prevent damage to the drill bit and unqualified drilled holes. After the drilling is completed, the aperture size and hole position accuracy of the through hole are checked.

[0024] Preferably, in step S3, the Plasma processing flow is as follows:

[0025] S31, generating high-energy plasma by a radio frequency generator;

[0026] S32, plasma contacts the surface of the flexible printed circuit board to remove contaminants, activate the surface and perform surface modification through physical and chemical effects;

[0027] Among them, Plasma treatment uses inert gas as the working gas. After the gas is ionized, it produces a material state composed of positively and negatively charged ions, molecules, atoms and atomic groups. Plasma treatment is used to remove dirt, oxides and burrs on the surface of flexible printed circuit boards, and increase the energy of the surface of flexible printed circuit boards to improve the adhesion between subsequent coatings or adhesives.

[0028] Preferably, in step S4, the first film application includes the following steps:

[0029] S41, placing the flexible printed circuit board on the workbench of the laminating machine, and fixing the flexible printed circuit board with a positioning fixture;

[0030] S42, placing the dry film on the flexible printed circuit board, and evenly laminating the dry film on the flexible printed circuit board using a roller or a pressing plate of a laminating machine;

[0031] S43. After laminating, check whether the dry film is completely attached to the surface of the flexible printed circuit board, and ensure that the dry film is evenly attached, without bubbles or wrinkles;

[0032] S44. Post-film processing: Leave the film for 15-30 minutes after application to avoid breakage or residue during exposure.

[0033] Preferably, in step S5, the flexible printed circuit board after full-sheet lamination is placed on a workbench of an exposure machine and fixed with a positioning fixture;

[0034] The first exposure operation is to adjust the exposure time and light intensity parameters of the exposure machine and use ultraviolet light to irradiate the film. The ultraviolet light penetrates the film base and irradiates the dry film, causing the photosensitive material on the dry film to react chemically.

[0035] First development: The exposed flexible printed circuit board is placed in a developer and developed using a low-concentration alkaline developer. During the development process, the unexposed part of the unpolymerized dry film will be dissolved in the developer, while the exposed and polymerized part will remain on the flexible printed circuit board.

[0036] Preferably, in step S6, during automatic optical inspection, the image of the through hole on the flexible printed circuit board is automatically scanned by a camera, the collected image is compared with the pre-set qualified through hole parameters, and the defects of the through hole on the flexible printed circuit board are detected by image processing technology to determine whether there is dimensional deviation or position offset, and the detected defects are displayed through a display or automatic marking for the operator to view and process.

[0037] Preferably, in step S7, the inspected flexible printed circuit board is hung on a hanger of an electroplating device, and the hanger is immersed in an electroplating solution, and copper ions are deposited on the surface of the flexible printed circuit board and in the through-holes by the action of an electric current to form a copper layer;

[0038] After the electroplating is completed, the flexible printed circuit board is taken out of the electroplating solution and cleaned and dried to remove residues and moisture on the surface of the flexible printed circuit board.

[0039] Preferably, in step S8, the electroplated flexible printed circuit board is immersed in a stripping liquid, and the temperature and soaking time of the stripping liquid are adjusted according to the thickness of the dry film, and then a stripping device is used to perform the stripping process. During the stripping process, the stripping liquid gradually dissolves the dry film and separates the dry film from the flexible printed circuit board.

[0040] Preferably, in step S10, the process of laser cleaning to remove the dry film residue in the hole is as follows: setting the laser coverage aperture to be 0.05 mm larger than the overall aperture of the through hole to ensure that the laser can fully cover the hole wall, and using a 0.15 mm aperture and a 0.5 mm spacing filling method for laser cleaning;

[0041] Finally, the laser parameters were set to 15 μJ pulse width*7 shots, meaning each through-hole received seven laser irradiations, each with a pulse width of 15 μJ, to remove the dry film residue in the through-hole.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] 1. The present invention uses a laser drill to clean the dry film in the hole, which can efficiently and accurately remove the dry film residue in the hole and improve production efficiency;

[0044] 2. The present invention can avoid damage to the copper surface and ensure the integrity of the FPC product by precisely controlling the laser energy and aperture size;

[0045] 3. The thorough cleaning of the dry film in the hole of the present invention can ensure the uniform filling of the resin during the subsequent lamination process of the flexible core board, avoid problems such as voids, cracking and delamination, and improve the reliability of FPC products;

[0046] 4. The present invention is applicable to various types of flexible printed circuit boards, especially FPC products with fine circuits or special impedance requirements. It is easy to operate and highly efficient, and is suitable for large-scale production applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is a flowchart of the present invention;

[0048] Figure 2 This is a flowchart of the process of cutting the flexible core board of the present invention;

[0049] Figure 3 This is a flowchart of the Plasma processing of the present invention;

[0050] Figure 4 This is a flowchart of the first film application of the present invention. DETAILED DESCRIPTION

[0051] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0052] See also Figure 1-4 , the present invention provides a technical solution: a cleaning method for through-hole electroplating of a flexible circuit board, comprising the following steps;

[0053] S1. Flexible core board cutting: According to the design requirements of the flexible printed circuit board, use professional cutting equipment to accurately cut the raw materials to obtain the required flexible board size;

[0054] In step S1, the process of cutting the flexible core board is as follows:

[0055] S11. Before cutting, check the flatness, thickness, surface damage and contaminants of the flexible board;

[0056] S12, parameter setting, setting the size, shape and precision of the flexible core board cutting, and adjusting the cutting speed, cutting depth and pressure parameters of the cutting machine;

[0057] S13. Positioning of flexible core board: Use the positioning fixture to fix the flexible core board on the working table of the cutting machine and ensure that the position and positioning angle of the flexible core board are correct;

[0058] S14. Cutting operation: Run the cutting machine to cut the flexible core board, and observe the cutting situation during the cutting process to ensure that the cutting depth and accuracy meet the requirements. If any abnormal situation occurs, such as insufficient cutting depth or position offset, stop the machine in time to adjust the parameters or repair the problem.

[0059] The FPC is inspected after cutting, including size, shape, precision and surface quality. The qualified FPCs are classified and marked according to the requirements of product design.

[0060] S2. Drilling: According to customer needs, through holes with a diameter of 0.15-0.3mm are drilled on the surface of the flexible printed circuit board using a drilling rig. A mechanical drilling rig with strong chip removal capability is used. Because the material of the FPC board is soft and has a low yield strength, it is easy to produce glue residue and melting during the drilling process.

[0061] In step S2, when drilling holes on the flexible printed circuit board, a drill bit with a diameter of 0.15-0.3 mm is selected and installed on the drilling rig, and the power and speed of the drill bit are controlled according to the thickness and hardness of the flexible printed circuit board to prevent damage to the drill bit and unqualified drilled holes. After the drilling is completed, the aperture size and hole position accuracy of the through hole are checked.

[0062] S3, Plasma treatment: Use plasma cleaning technology to clean the soft board after drilling, remove burrs, dirt and oxides generated during the drilling process, and ensure the hole wall is smooth and clean;

[0063] In step S3, the Plasma processing flow is as follows:

[0064] S31, generating high-energy plasma by a radio frequency generator;

[0065] S32, plasma contacts the surface of the flexible printed circuit board to remove contaminants, activate the surface and perform surface modification through physical and chemical effects;

[0066] Surface cleaning: Plasma treatment can effectively remove pollutants on the FPC surface, such as organic solvent residues, oxides and particulate matter, providing a clean surface for subsequent process steps;

[0067] Surface activation: Plasma treatment can increase the energy of the FPC surface and improve its adhesion with subsequent coatings or adhesives;

[0068] Surface modification: Plasma treatment can change the chemical properties of the FPC surface, giving it specific functionality, such as hydrophilicity, hydrophobicity or antistatic properties.

[0069] Among them, Plasma treatment uses inert gas as the working gas. After the gas is ionized, it produces a material state composed of positively and negatively charged ions, molecules, atoms and atomic groups. Plasma treatment is used to remove dirt, oxides and burrs on the surface of flexible printed circuit boards, and increase the energy of the surface of flexible printed circuit boards to improve the adhesion between subsequent coatings or adhesives.

[0070] During the plasma treatment process, it is necessary to control parameters such as plasma power, treatment time, gas type and flow rate to obtain the best treatment effect.

[0071] Plasma processing requires avalanche ionization under the action of a strong electric field, and this transformation is a transition from an insulator to a semiconductor.

[0072] Plasma treatment does not cause mechanical damage to FPC, can quickly remove surface pollutants and oxides, uses inert gas as working gas, and does not produce harmful substances.

[0073] S4. First lamination: Lamination is performed on the entire flexible printed circuit board after cleaning, ensuring that the dry film is evenly covered on the board surface without bubbles;

[0074] The preparation work before the first film lamination is as follows: confirm whether the cleanliness, flatness and size of the FPC board meet the requirements, select the appropriate dry film material according to the size of the FPC board and the circuit design, and ensure that the dry film is not damaged or contaminated. Ensure that the film lamination environment is clean, dust-free and free of impurities to avoid affecting the quality of the film lamination;

[0075] Use cleaning tools to remove impurities and oxides on the surface of the flexible printed circuit board to ensure that the directional holes of the flexible printed circuit board are in the same position for subsequent alignment and exposure operations.

[0076] In step S4, the first film application includes the following steps:

[0077] S41. Place the flexible printed circuit board on the workbench of the laminating machine and use a positioning fixture to fix the flexible printed circuit board to ensure that the flexible printed circuit board is positioned accurately;

[0078] S42. Place the dry film on the flexible printed circuit board and evenly adhere the dry film to the flexible printed circuit board using the roller or press plate of the laminating machine; pay attention to controlling the temperature, pressure, rotation speed and other parameters of the roller to ensure the quality of the laminating.

[0079] S43. After laminating, check whether the dry film is completely attached to the surface of the flexible printed circuit board, and ensure that the dry film is evenly attached, without bubbles or wrinkles;

[0080] S44. Post-film processing: Leave the film for 15-30 minutes after application to avoid breakage or residue during exposure.

[0081] S5. First exposure and development: Through the exposure and development process, the unnecessary parts on the dry film are removed to expose the through-hole positions that need to be electroplated;

[0082] Preparation before exposure: Check whether the exposure equipment is in good working condition, ensure that the light source and optical path system in the exposure machine are normal, and prepare graphic data in positive or negative form. These data already contain the position information of the through holes that need to be electroplated.

[0083] In step S5, the flexible printed circuit board after full-sheet lamination is placed on a workbench of an exposure machine and fixed with a positioning fixture;

[0084] The first exposure operation is to adjust the exposure time, light source intensity parameters, and other parameters of the exposure machine. The settings of these parameters depend on the material of the FPC board, the photosensitivity of the dry film, and the designed circuit pattern. Ultraviolet light is used to irradiate the dry film. The ultraviolet light penetrates the film base and irradiates the dry film, causing a chemical reaction in the photosensitive material on the dry film.

[0085] After the exposure is completed, the FPC board is preliminarily inspected to ensure uniform exposure without any omission or overexposure. If necessary, the parameters of the exposure machine are adjusted or the exposure is repeated according to the inspection results.

[0086] First development: prepare the developing equipment and developer, ensure that the developer is within the validity period and the concentration is appropriate, place the exposed flexible printed circuit board into the developer, and use a low-concentration alkaline developer for development. During the development process, the unexposed part of the unpolymerized dry film will be dissolved in the developer, and the exposed and polymerized part will remain on the flexible printed circuit board.

[0087] And control the concentration, temperature, development time and other parameters of the developer to ensure uniform development and avoid excessive dissolution of the polymerized parts.

[0088] After development is completed, use clean water to clean the FPC sheet to remove residual developer and impurities, and use a dryer or natural drying method to dry the FPC sheet to avoid residual moisture affecting subsequent processes.

[0089] S6. Automatic optical inspection: Use automatic optical inspection equipment to inspect the flexible printed circuit board after exposure and development to ensure the accuracy of the through-hole dry film window pattern and the cleanliness of the through-hole;

[0090] In step S6, during automatic optical inspection, the camera automatically scans the image of the through-hole on the flexible printed circuit board, compares the collected image with the pre-set qualified through-hole parameters, and uses image processing technology to detect defects in the through-hole on the flexible printed circuit board, whether there is dimensional deviation or position offset, and displays the detected defects through a display or automatic marking for the operator to view and process.

[0091] S7, thin plate vertical continuous electroplating (hole copper plating): the qualified flexible printed circuit board is sent to the thin plate vertical continuous electroplating equipment for hole copper plating. Through electroplating, it is ensured that the inner wall of the through hole is evenly covered with a layer of copper;

[0092] In step S7, the inspected flexible printed circuit board is hung on a hanger of an electroplating device, and the hanger is immersed in an electroplating solution. The copper ions are deposited on the surface of the flexible printed circuit board and in the through-holes by the action of an electric current to form a copper layer.

[0093] After the electroplating is completed, the flexible printed circuit board is taken out of the electroplating solution and cleaned and dried to remove residues and moisture on the surface of the flexible printed circuit board.

[0094] Finally, the electroplated flexible printed circuit board is subjected to quality inspection, including appearance inspection, thickness measurement and conductivity test, to ensure that the quality of the electroplating layer meets the requirements.

[0095] Since the electroplating process is continuous, it can greatly improve production efficiency. The vertically suspended flexible printed circuit board makes the electroplating layer more uniform, especially in the holes, which can ensure the consistent thickness of the copper layer on the hole wall.

[0096] S8, film stripping: After the electroplating is completed, the flexible printed circuit board is stripped to remove the unnecessary dry film on the circuit board;

[0097] In step S8, the electroplated flexible printed circuit board is immersed in a stripping liquid, and the temperature and soaking time of the stripping liquid are adjusted according to the thickness of the dry film. Then, a stripping device is used to perform the stripping process. During the stripping process, the stripping liquid gradually dissolves the dry film and separates the dry film from the flexible printed circuit board.

[0098] After film stripping is complete, remove the FPC board from the stripping solution and place it in a water washing machine for cleaning. The purpose of cleaning is to remove any residual film stripping solution and dried film fragments from the FPC board. Use deionized or purified water to rinse the FPC board multiple times to ensure the surface is clean and free of residue. After cleaning, place the FPC board in a drying machine for drying. Drying removes moisture from the FPC board to prevent rust and moisture.

[0099] S9, pattern transfer process: After the film is removed, the pattern transfer process is carried out. The pattern transfer process includes the second film application, exposure and development to form the final circuit pattern;

[0100] S10. Laser cleaning to remove dry film residue in the hole: Use a laser drill to clean the dry film residue in the hole to remove the dry film residue in the hole.

[0101] In step S10, the process of laser cleaning to remove the dry film residue in the hole is as follows: setting the laser coverage aperture to be 0.05 mm larger than the overall through-hole aperture to ensure that the laser can fully cover the hole wall, and using a 0.15 mm aperture and a 0.5 mm spacing filling method for laser cleaning;

[0102] Finally, the laser parameters were set to 15 μJ pulse width*7 shots, meaning each through-hole received seven laser irradiations, each with a pulse width of 15 μJ, to remove the dry film residue in the through-hole.

[0103] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for cleaning through-hole electroplating of a flexible circuit board, characterized in that: The following steps are included: S1. Flexible core board cutting: According to the design requirements of the flexible printed circuit board, use professional cutting equipment to accurately cut the raw materials to obtain the required flexible board size; S2. Drilling: Drill through holes with a diameter of 0.15-0.3mm on the flexible printed circuit board according to customer requirements; S3, Plasma treatment: Use plasma cleaning technology to clean the soft board after drilling, remove burrs, dirt and oxides generated during the drilling process, and ensure the hole wall is smooth and clean; S4. First lamination: Lamination is performed on the entire flexible printed circuit board after cleaning, ensuring that the dry film is evenly covered on the board surface without bubbles; S5. First exposure and development: Through the exposure and development process, the unnecessary parts on the dry film are removed to expose the through-hole positions that need to be electroplated; S6. Automatic optical inspection: Use automatic optical inspection equipment to inspect the flexible printed circuit board after exposure and development to ensure the accuracy of the through-hole dry film window pattern and the cleanliness of the through-hole; S7, thin plate vertical continuous electroplating (hole copper plating): the qualified flexible printed circuit board is sent to the thin plate vertical continuous electroplating equipment for hole copper plating. Through electroplating, it is ensured that the inner wall of the through hole is evenly covered with a layer of copper; S8, film stripping: After the electroplating is completed, the flexible printed circuit board is stripped to remove the unnecessary dry film on the circuit board; S9, pattern transfer process: After the film is removed, the pattern transfer process is carried out. The pattern transfer process includes the second film application, exposure and development to form the final circuit pattern; S10. Laser cleaning to remove dry film residue in the hole: Use a laser drill to clean the dry film residue in the hole to remove the dry film residue in the hole.

2. A method for cleaning through-hole electroplating of a flexible circuit board according to claim 1, characterized in that: In step S1, the process of cutting the flexible core board is as follows: S11. Before cutting, check the flatness, thickness, surface damage and contaminants of the flexible board; S12, parameter setting, setting the size, shape and precision of the flexible core board cutting, and adjusting the cutting speed, cutting depth and pressure parameters of the cutting machine; S13. Positioning of flexible core board: Use the positioning fixture to fix the flexible core board on the working table of the cutting machine and ensure that the position and positioning angle of the flexible core board are correct; S14, cutting operation: operate the cutting machine to cut the flexible core board and observe the cutting condition during the cutting process.

3. The method for cleaning through-hole electroplating of a flexible circuit board according to claim 1, characterized in that: In step S2, when drilling holes on the flexible printed circuit board, a drill bit with a diameter of 0.15-0.3 mm is selected and installed on the drilling rig, and the power and speed of the drill bit are controlled according to the thickness and hardness of the flexible printed circuit board to prevent damage to the drill bit and unqualified drilled holes. After the drilling is completed, the aperture size and hole position accuracy of the through hole are checked.

4. The method for cleaning through-hole electroplating of a flexible circuit board according to claim 1, wherein: In step S3, the Plasma processing flow is as follows: S31, generating high-energy plasma by a radio frequency generator; S32, plasma contacts the surface of the flexible printed circuit board to remove contaminants, activate the surface and perform surface modification through physical and chemical effects; Among them, Plasma treatment uses inert gas as the working gas. After the gas is ionized, it produces a material state composed of positively and negatively charged ions, molecules, atoms and atomic groups. Plasma treatment is used to remove dirt, oxides and burrs on the surface of flexible printed circuit boards, and increase the energy of the surface of flexible printed circuit boards to improve the adhesion between subsequent coatings or adhesives.

5. The method for cleaning through-hole electroplating of a flexible circuit board according to claim 1, characterized in that: In step S4, the first film application includes the following steps: S41, placing the flexible printed circuit board on the workbench of the laminating machine, and fixing the flexible printed circuit board with a positioning fixture; S42, placing the dry film on the flexible printed circuit board, and evenly laminating the dry film on the flexible printed circuit board using a roller or a pressing plate of a laminating machine; S43. After laminating, check whether the dry film is completely attached to the surface of the flexible printed circuit board, and ensure that the dry film is evenly attached, without bubbles or wrinkles; S44. Post-film processing: Leave the film for 15-30 minutes after application to avoid breakage or residue during exposure.

6. The method for cleaning through-hole electroplating of a flexible circuit board according to claim 1, characterized in that: In step S5, the flexible printed circuit board after full-sheet lamination is placed on a workbench of an exposure machine and fixed with a positioning fixture; The first exposure operation is to adjust the exposure time and light intensity parameters of the exposure machine and use ultraviolet light to irradiate the film. The ultraviolet light penetrates the film base and irradiates the dry film, causing the photosensitive material on the dry film to react chemically. First development: The exposed flexible printed circuit board is placed in a developer and developed using a low-concentration alkaline developer. During the development process, the unexposed part of the unpolymerized dry film will be dissolved in the developer, while the exposed and polymerized part will remain on the flexible printed circuit board.

7. The method for cleaning through-hole electroplating of a flexible circuit board according to claim 1, characterized in that: In step S6, during automatic optical inspection, the camera automatically scans the image of the through-hole on the flexible printed circuit board, compares the collected image with the pre-set qualified through-hole parameters, and uses image processing technology to detect defects in the through-hole on the flexible printed circuit board, whether there is dimensional deviation or position offset, and displays the detected defects through a display or automatic marking for the operator to view and process.

8. The method for cleaning through-hole electroplating of a flexible circuit board according to claim 1, characterized in that: In step S7, the inspected flexible printed circuit board is hung on a hanger of an electroplating device, and the hanger is immersed in an electroplating solution. The copper ions are deposited on the surface of the flexible printed circuit board and in the through-holes by the action of an electric current to form a copper layer. After the electroplating is completed, the flexible printed circuit board is taken out of the electroplating solution and cleaned and dried to remove residues and moisture on the surface of the flexible printed circuit board.

9. The method for cleaning through-hole electroplating of a flexible circuit board according to claim 1, characterized in that: In step S8, the electroplated flexible printed circuit board is immersed in a stripping liquid, and the temperature and soaking time of the stripping liquid are adjusted according to the thickness of the dry film. Then, a stripping device is used to perform the stripping process. During the stripping process, the stripping liquid gradually dissolves the dry film and separates the dry film from the flexible printed circuit board.

10. The method for cleaning through-hole electroplating of a flexible circuit board according to claim 1, characterized in that: In step S10, the process of laser cleaning to remove the dry film residue in the hole is as follows: setting the laser coverage aperture to be 0.05 mm larger than the overall through-hole aperture to ensure that the laser can fully cover the hole wall, and using a 0.15 mm aperture and a 0.5 mm spacing filling method for laser cleaning; Finally, the laser parameters were set to 15 μJ pulse width*7 shots, meaning each through-hole received seven laser irradiations, each with a pulse width of 15 μJ, to remove the dry film residue in the through-hole.

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